Auxiliary combustion chamber for internal combustion engine

ABSTRACT

An auxiliary combustion chamber at least partially embedded in the cylinder head of an internal combustion engine adjacent the intake valve of a main combustion chamber and having a spark plug positioned in the auxiliary chamber and unvalved inlet and outlet ports interconnecting the auxiliary chamber with the main chamber. The air/fuel mixture drawn into the main combustion chamber is deflected by the back surface of the intake valve into the inlet port of the auxiliary combustion chamber toward the spark plug. The auxiliary combustion chamber may include a shell positioned in a cavity in the cylinder head with devices for properly positioning the shell in the cavity and for retaining the shell and preventing it from rotating. A passage is provided for rich air/fuel mixture terminating at the rear surface of the valve, when closed, with refinements of the passage, shape of the inlet port, and main combustion chamber wall facilitating the flow of the rich mixture into the auxiliary combustion chamber by venturi action. The flow of fresh mixture into the auxiliary combustion chamber through suction scavenges the combustion gas remaining from the prior firing sequence.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to auxiliary combustion chambers for internalcombustion engines and more particularly to unvalved auxiliarycombustion chambers at least partially embedded in the cylinder head.

2. Background of the Invention

Various means for removing toxic substances contained in the exhaustgases of internal combustion engines have been proposed. Among them isincluded apparatus that burns a lean air/fuel mixture. This is one ofthe very effective measures, achieved by taking notice of the fact thatcombustion of a lean air/fuel mixture, in which the ratio of air to fuelis high, reduces such toxic substances, especially nitrogen oxides, inthe exhaust gases.

However, a lean air/fuel mixture usually gives rise to misfiring andlowers thermal efficiency of the engine cycle, because of the lowignitability and slow flame-propagation speed. To overcome thisshortcoming, it has been proposed to provide an auxiliary combustionchamber in addition to the main combustion chamber, so that a leanair/fuel mixture in the main combustion chamber is ignited by the torchflame blown from the auxiliary combustion chamber. In a typicalembodiment of this type, the auxiliary combustion chamber is equippedwith an intake valve to admit a relatively rich air/fuel mixture, whichis ignited by a spark plug, and then a lean air/fuel mixture in the maincombustion chamber is burnt by the torch flame from the auxiliarycombustion chamber. This type of arrangement is very effective but theconstruction of the auxiliary chamber is very complex because of thenecessity of an auxiliary intake valve.

It has also been proposed that an auxiliary combustion chamber having nointake valve be positioned in the main combustion chamber. During thecompression stroke, lean air/fuel mixture in the main combustion chamberis forced into the auxiliary combustion chamber, where it is ignited bya spark plug. Then, the flame produced is blown back into the maincombustion chamber to burn the lean air/fuel mixture therein. Thisarrangement has the defects that the residual gases from the precedingstrike remain in the auxiliary combustion chamber making the ignition onnext strike difficult and the lean air/fuel mixture is, itself,difficult to fire.

In the internal combustion engine having an auxiliary combustion chamberof this type, additionally the temperature in the auxiliary combustionchamber becomes excessively high because the auxiliary combustionchamber is not only exposed to high temperature gases for a long time,since ignition and combustion starts therefrom, but also is subjected tothe influence of heat radiated through the flame nozzle providedtherein. As a consequence, such undesirable phenomena become liable tooccur as premature ignition and a reduction in the durability of theauxiliary combustion chamber against high temperature. It is, therefore,necessary to provide the auxiliary combustion chamber with the capacityto withstand high temperature and to dissipate the heat accumulatedtherein.

SUMMARY OF THE INVENTION

It is therefore, the primary object of this invention to improveauxiliary combustion chambers for internal combustion engines.

It is another object of this invention to supply an auxiliary combustionchamber with an enriched air/fuel mixture without a complex valveconstruction.

It is a further object of this invention to scavenge from an unvalvedauxiliary combustion chamber the combustion gases from one firingsequence before the succeeding firing sequence.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and attained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

To achieve the foregoing objects and in accordance with the purpose ofthe invention, as embodied and broadly described herein, this inventioncomprises an auxiliary combustion chamber integrally cast in the wall ofthe cylinder head of an internal combustion chamber adjacent theair/fuel mixture intake of a main combustion chamber and having thespark gap of a spark plug positioned in the auxiliary combustionchamber; and an unvalved inlet port interconnecting the auxiliarychamber and the main chamber for conducting air/fuel mixture into theauxiliary chamber and an unvalved outlet port for conducting residualcombustion gas from the auxiliary chamber to the main chamber.

Preferably, tubular inserts of heat and corrosion-resisting material arefixed within the inlet and outlet ports.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Of the drawings:

FIG. 1 is a cross-sectional view of an auxiliary combustion chamberaccording to this invention, which is integrally cast inside thecylinder head.

FIG. 2 is a portion of the auxiliary combustion chamber of FIG. 1including heat and corrosion resisting inserts in the unvalved inlet andoutlet ports.

FIG. 3 is a cross-sectional view of a combustion chamber representing anembodiment of this invention, including an auxiliary combustion chambershell in a cavity in the cylinder head.

FIG. 4 is a bottom view of the auxiliary combustion chamber shell shownin FIG. 3.

FIG. 5 is a cross-sectional view of another embodiment of this inventionincluding apparatus for positioning an auxiliary combustion shell in acavity in the cylinder head.

FIG. 6 is a cross-sectional view of still another embodiment of thisinvention showing devices for correctly positioning and retaining anauxiliary combustion shell in a cylinder head.

FIG. 7 is a cross-sectional view of the embodiment of FIG. 6 wherein thepositioning device has been replaced by the spark plug.

FIG. 8 is a cross-sectional view of a further embodiment of thisinvention.

FIG. 9 is a cross-sectional view of the auxiliary combustion chambershell of FIG. 8.

FIG. 10 is a bottom view of one embodiment for the shape for an inletport of the shell of FIG. 8.

FIG. 11 is a cross-sectional view of the auxiliary combustion chambershell of FIG. 8.

FIG. 12 is a bottom view of a second embodiment for the shape of aninlet port for the shell of FIG. 8.

FIG. 13 is a cross-sectional view of still another embodiment of thisinvention.

FIG. 14 is a schematic bottom view of the embodiment of FIG. 13including the exhaust valve taken along lines A--A of FIG. 13.

FIG. 15 is a cross-sectional view of the auxiliary combustion chamberand an embodiment of the enriched air/fuel input of the invention.

FIG. 16 is a partial view of a variation of the enriched air/fuel inputof FIG. 15.

FIG. 17 is another embodiment of the enriched air/fuel input of FIG. 15.

FIG. 18 is an enlarged front view taken along line A--A of FIG. 17.

FIG. 19 is still another embodiment of the enriched air/fuel input ofFIG. 15.

FIG. 20 is a cross-sectional view of the auxiliary combustion chamberand a different embodiment of the air/fuel input of the invention.

FIG. 21 is an enlarged partial view taken along the line A--A of FIG.20.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings.

Referring now to FIGS. 1 and 2, a main combustion chamber 20 is shown ina cylinder head 22 together with an intake valve 24 for admitting amixture of air and fuel into the combustion chamber.

In accordance with the invention, an auxiliary combustion chamber 26,having no intake valve, is integrally cast within the cylinder head 22.An inlet port 28 opens toward a stream of air/fuel mixture P admitted bythe intake valve 24 and deflected toward the inlet port 28 by the backsurface 30 of the valve. The inlet port 28 and an outlet port 32interconnect the auxiliary chamber 26 with the main chamber 20. A sparkplug 34 has its spark gap 36 positioned in the auxiliary combustionchamber 26.

Preferably, in the casting of the cylinder head, the portion of the wallof the main combustion chamber including the inlet and outlet ports isformed to extend slightly outwardly into the main combustion chamber.The inlet port 28 is then preferably angled toward the intake ofair/fuel mixture of the main combustion chamber for facilitating theflow of incoming mixture into the port 28.

On being deflected by the back surface 30 of the valve 24, part of theincoming mixture becomes the stream P that is introduced into theauxiliary combustion chamber 26 through the inlet port 28. This streamof incoming mixture P may be mixed with rich air/fuel mixture suppliedfrom a pipe 42. As the air/fuel mixture is drawn into the auxiliarycombustion chamber on the intake stroke of the piston, the residualcombustion gas of the preceding firing stroke is scavenged, i.e., sweptout, through the outlet port 32, as indicated by the arrow Q. Then, onthe compression stroke, the intake valve 24 closed the intake supply 40including the rich air/fuel mixture supply pipe 42, thereby stopping thesupply of the rich air/fuel mixture to the main combustion chamber 20,and further, preventing said mixture from stagnating in the incomingmixture passage. At the conclusion of the compression stroke, a portionof the lean air/fuel mixture in the main combustion chamber 20 is forcedinto the auxiliary combustion chamber 26 where it is intermingled withthe rich mixture compressed and ignited by the spark plug 34. Then, thetorch flame blown through the ports 28 and 32 ignites the lean air/fuelmixture in the main combustion chamber 20.

When the cylinder head 22 is made of such light alloy as aluminum thatis low in heat and corrosion resistivity at high temperature, tubeinserts 38, made of such heat and corrosion resisting material asstainless steel or ceramics, may be fixed inside the ports 28, 32,connecting the auxiliary and main combustion chambers 26 and 20, asshown in FIG. 2. Since heat load becomes highest in the inlet port 28and outlet port 32, erosion due to excessive heat and damages due tohigh temperature corrosion are most likely to occur in these areas andare minimized by inserts 38.

The invention, embodied as described above, can achieve the followingremarkable effects. Because the auxiliary combustion chamber isintegrally cast within the cylinder head, transmission of heat therefromcan be attained smoothly, thereby improving the effect of its heatradiation. Further, it is unnecessary to use any costly heat resistingalloy for the auxiliary combustion chamber. When the cylinder head ismade of such light alloy as aluminum alloy that is more readily affectedby heat, heat resisting material need be used only in the inlet andoutlet ports, where heat load becomes maximum, with a view to reducingthe manufacturing cost.

On the induction stroke of the engine the intake valve 24 opens, andlean air/fuel mixture is drawn by suction into the main combustionchamber 20 through the incoming mixture passage 40. In accordance withthe invention, a rich air/fuel mixture is supplied as part of the streamof incoming mixture, by use of a rich air/fuel mixture supply pipe 42.As embodied herein, the end of said pipe 42 is designed to be closed bythe back surface of the valve 24 so that the rich air/fuel mixturecannot flow when the intake valve 24 is closed.

In accordance with the invention, as shown in FIGS. 3 and 4, theauxiliary combustion chamber of the invention may be attained byinserting an auxiliary combustion chamber shell 46 in a cavity 48 formedin the cylinder head 22. As embodied herein, the auxiliary combustionchamber shell 46 is formed with a flange 50 cooperating with a channel51 in the cylinder head to retain the shell in the cavity. A flattenedarea 52 is formed on the flange 50 for cooperating with complementaryabutment in the channel 51 for positioning the shell 46 and preventingthe shell from rotating. The shell 46 may be integrally fitted in thecylinder head 22 by inserting the shell into the mold when casting thecylinder head.

Means for preventing the auxiliary combustion chamber shell 6 fromrotation of coming out of the cylinder head are not limited to onesshown in FIG. 4, but may include a roughened surface, a groove, or anyother suitable means.

Preferably, the cavity 48 is formed as a right circular cylinder andpositioned eccentrically in the cylinder head with respect to the axisof the cylinder for aligning the inlet port 28 more efficiently with theintake 40 of the main combustion chamber.

The auxiliary combustion chamber shell of the invention increases theefficiency with which the heat generated in the auxiliary combustionchamber is transmitted thereby increasing the durability of theauxiliary combustion chamber shell. Also, it is unnecessary to use anycostly, heat-resisting alloy for the auxiliary combustion chamber shellof this type.

The use of the auxiliary combustion chamber shell is suited particularlyfor gasoline engines in which the temperature becomes high, but is alsosuited for diesel engines. Being inserted when casting the cylinderhead, the auxiliary combustion chamber of this invention has higher heattransmission efficiency, as compared with others fitted in the cylinderhead by press-fitting or other methods. This facilitates the cooling ofthe auxiliary combustion chamber shell, which in turn reduces theinfluence of heat load. Therefore, even an auxiliary combustion chambershell made of low-cost metal can insure sufficient durability.

In accordance with the invention, as shown in FIG. 5, the auxiliarycombustion shell 46 may be retained in the cavity 48 of the cylinderhead 22 by the threaded portion of the spark plug 34 and may beprevented from rotating by a pin threaded into the cylinder head andengaging a notch in the outside surface of the shell.

As embodied herein, the cavity 48 may be formed substantially as a rightcircular cylinder and be interconnected to the outside of the cylinderhead by a cylindrical aperture 53 having an enlarged outward portion 54forming a shoulder 55 for receipt of a standard spark plug. Theauxiliary combustion chamber shell 46 may be complementary in shape tothe cylindrical cavity 48 and has a threaded aperture 56 for receivingthe threaded portion 58 of the spark plug 34 axially aligned in thecylindrical cavity.

It is, of course, essential that the inlet port 28 to the auxiliarycombustion chamber 26 be properly aligned with the air/fuel mixturebeing deflected by the back surface 30 of the valve 24. The shell 46must therefore be properly positioned in the cavity 48 and must bemaintained securely in the proper position.

As embodied herein, the cylindrical outside surface of the shell 46 maybe provided with a slot or notch 60 which identifies the proper positionof the shell 46. In addition, the notch 60 may permanently receive theend of a pin 61 threaded through the cylinder head for preventing anyshifting in position of the shell 46.

Alternatively, as embodied herein and depicted in FIGS. 6 and 7, thecylindrical base 62 of the auxiliary combustion chamber shell 46 may beprovided with two threaded apertures-- one 64 axially through the base66 of the cylindrical shell and another 68 through the curved surface ofthe shell.

The aperture 68 through the curved surface of the shell 46 is both forthe purpose of properly positioning the shell 46 and for the receipt ofthe spark plug 34. The aperture 64 is utilized to receive a retainingbolt 70 through the cylinder wall 22 after the shell 46 is properlypositioned.

Preferably the aperture 68 and its aligned bore 72 through the wall ofthe cylinder head 22 are angled toward the inlet port 28 of theauxiliary combustion chamber 26. An auxiliary positioning device such asbolt 74 may be utilized for precisely locating the shell 46 in thecavity 48 and then removed for insertion of the spark plug 34.

Alternatively, the spark plug 34 itself may be used for the additionaltwo purposes of properly locating the shell 46 in the cavity 48 and forretaining the shell against rotation in the cavity.

By locating the spark plug in the side of the shell 46 and angling itsdirection toward the inlet port 28, the efficiency of the auxiliarycombustion chamber 26 is increased. The direction of the focus of therich air/fuel mixture deflected into the auxiliary combustion chamber 26may be further guided and the scavenging effect of the air/fuel flowincreased by the formation of a projection 76 on the internal surface ofthe shell 46 between the inlet port 28 and the outlet port 32. Such aprojection 76 serves not only to direct the flow of the incomingair/fuel mixture but to reduce the turbulence in the shell 26 withimproved flow of exhausted gases outwardly through the port 32.

In accordance with the invention, as shown in FIG. 8, the auxiliarycombustion chamber shell 46 may be inserted into the cavity 48 in thecylinder head 22 through a bore 78, of larger diameter than thecylindrical cavity 48, extending through the wall of the cylinder head.

As herein embodied, the shell 46 has a flange 80 fitting into an annularnotch 82 formed in the shoulder 84 between the periphery of the cavity48 and the surface of the bore 78. A portion of the flange 80 may beflattened or cut away, as shown at 52 in FIG. 4, to form a positioningdevice when interacting with a complementary surface (not shown) formedin the annular notch 82.

As herein embodied, a cylindrical block 86 is inserted in the bore 78flush against the flange 80 for retaining the shell 46 in properposition with the inlet port 28 and outlet port 32 extending into themain combustion chamber 20 and the inlet port 28 aligned to receive thestream P of air/fuel mixture. The block 86 may be secured in the bore 78as by bolts 88 threaded into the cylinder head 22.

The spark plug 34 is axially threaded into the block 86 to have itsspark gap 36 in the auxiliary combustion chamber 26.

In accordance with the invention, it is advantageous to design the shapeof the inlet port 28 so that the stream of air/fuel mixture P may beintroduced efficiently. The stream of air/fuel mixture P, deflected bythe back 30 of the valve 24, flows from the periphery of the intake 40along the internal wall of the main combustion chamber 20. The richair/fuel mixture supplied from the pipe 42 also tends to spread alongthe periphery of the intake 40. In the embodiment as shown in FIGS. 9and 10, the shape of the inlet port 28 has been widened along theperiphery of the air/fuel mixture intake 40. The elliptical shape 90 ofthe inlet port 28 introduces the stream of air/fuel mixture P moreefficiently than a perfectly circular shape. This combination ofelements remarkably improves the operational stability and reliabilityof internal combustion engines utilizing an auxiliary combustion chamberhaving no intake valve. It is also desirable to form the inlet port 28in such a shape as to produce as little abrasion resistance in the inletas possible.

In the embodiment shown in FIGS. 11 and 12, the shape of the inlet port28 is formed as a trumpet 92, with its cross-sectional areaprogressively decreasing along the passage of the incoming air/fuelmixture running from the main combustion chamber side to the auxiliarycombustion chamber side.

In this embodiment, resistance to the incoming air/fuel mixture isdecreased and the scavenging efficiency of the auxiliary combustionchamber is improved, compared with other combustion chambers where theincoming mixture passage is uniform in cross-sectional area throughoutits entire length.

In accordance with the invention, the efficiency of the auxiliarycombustion chamber 46 may be further improved by recessing the intake 40from the interior wall surface of the main combustion chamber 20 topromote better communication of the incoming air/fuel mixture betweenthe intake 40 and the inlet port 28. Additionally, when the wall of themain combustion chamber is recessed slightly at the intake 40, theauxiliary combustion chamber shell 46 may be projected less into themain combustion chamber, thereby increasing the durability of theauxiliary combustion chamber through the lowering of its thermal load,and enabling the use of lower cost material for the auxiliary combustionchamber shell.

As embodied in FIGS. 13 and 14, the main combustion chamber 20 isdefined by a piston 94 and the cylinder head 22. The air/fuel mixture isintroduced into the combustion chambers through the intake valve 24 andthe combustion gas is discharged through an exhaust valve 96.

In accordance with the invention, the wall of the main combustionchamber 20 is recessed around the intake 40 of the passage 98 used tosupply the lean air/fuel mixture into the combustion chamber. A recessedsurface 100 is thus formed around the intake 40, thus permitting thevalve seat 102 and the valve 24 to be slightly recessed into the wall ofthe main combustion chamber 20 for facilitating the flow of thedeflected portion of the air/fuel mixture into the inlet port 28.

As previously described, a projection 76 is formed on the wall of theauxiliary combustion chamber shell 46 between the inlet port 28 and theoutlet port 32 for increasing the scavenging effect of the gas flow.Although only two inlet and outlet ports are shown for the shell 46, itis understood that a larger number may be utilized if desired. The pipe42, terminating at the opening 44, conducts a rich air/fuel mixture tothe outlet 40 and is closed by the back surface 30 of the valve 24 whenthe valve is closed, as previously described. The rich air/fuel mixtureis drawn into the main chamber 20 and the auxiliary chamber 26 bysuction along with the lean air/fuel mixture through the intake 40 andis then deflected into the inlet port by the back surface 30 of thevalve 24, as previously described.

The operation of this invention thus composed, as embodied in FIGS. 13and 14, may be described as follows:

As the piston 94 enters its suction stroke, the intake valve 24 opensand a lean air/fuel mixture is introduced into the main combustionchamber 20 through the intake 40. A rich air/fuel mixture also isintroduced into the main combustion chamber 20 through the passage 42.Being deflected by the back face 30 of the intake valve 24, part of thestream of incoming air/fuel mixture flows as indicated by the arrow P.The inlet port 28 made in the auxiliary combustion chamber shell 46 isaimed toward the deflected stream of incoming mixture, and the stream ofincoming mixture is directed into the auxiliary combustion chamber 26.As a consequence, the residual combustion gas of the preceding stroke isscavenged through the outlet port 32 as indicated by the arrow Q. Theprojection 76 formed in the auxiliary combustion chamber shell 26eliminates turbulence of the scavenging stream in the auxiliarycombustion chamber 26, thereby preventing the fresh mixture introducedas the scavenging mixture from mixing with the residual combustion gasproduced during the preceding stroke.

On entering the compression stroke, the intake valve 24 is received inthe valve seat 102 to close the intake port opening 40. As the piston 94elevates, the lean air/fuel mixture in the main combustion chamber isforced into the auxiliary combustion chamber 26, where it is mixed withthe rich mixture, compressed and then ignited by the spark plug 34. Theflame produced in the auxiliary combustion chamber 26 is then blown intothe main combustion chamber 20, through the ports 28, 32 to ignite thelean air/fuel mixture therein.

In the above-described operation, communication between incoming streammixture and the inlet port 28 can be insured, according to theinvention, since the intake opening 40 is recessed from the ordinarysurface of inner wall defining the main combustion chamber 20. Also, theauxiliary combustion chamber shell 46 of this embodiment is projectedless into the main combustion chamber 20.

In the above-described embodiments, the intake passage 98 and the pipe42 are provided to supply the lean and rich, air/fuel mixtures,respectively. The purpose of this is to achieve stable combustion evenwhen the total air/fuel ratio in the cylinder becomes very high (forexample, the air/fuel ratio of 22 to 24 to 1), by effectively supplyingthe right air/fuel mixture into the auxiliary combustion chamber throughsaid pipe 42. However, the auxiliary chamber of the invention isoperative without the addition of a rich mixture if only a lean mixtureis desired.

As described previously, this invention ensures not only scavenging ofthe auxiliary combustion chamber but also ignition of the air/fuelmixture therein. By the use of the torch flame supplied from theauxiliary combustion chamber, the lean air/fuel mixture is burnt rapidlyand completely, which results in a reduction in the nitrogen oxidecontent in the exhaust gases. By decreasing the thermal load imposed onthe auxiliary combustion chamber shell, durability of the shell isincreased. Also, this makes it possible to use low-cost material for theauxiliary combustion chamber shell.

In accordance with the invention, the ignition of the rich air/fuelmixture in the auxiliary combustion chamber is further improved bypreheating the rich air/fuel mixture by passing in through a bore in thecylinder head. Additionally, the provision of a passage for the richair/fuel mixture is simplified and the manufacture and assembly of therich air/fuel mixture supplying apparatus facilitated.

As embodied herein and shown in FIG. 15, a bore 106 is provided in thecylinder head 22 as a passageway for the rich air/fuel mixture to beutilized as part of the incoming stream P drawn into the auxiliarycombustion chamber 26. A short tube 108 conducts the rich air/fuelmixture from the bore 106 into the intake opening 40. The mouth of thetube 108 is positioned adjacent the inlet port 28 of the shell 46 and isclosed by the back surface 30 of the valve 24 when the valve is closed.

As embodied herein, the tube 108 may be affixed in the bore 106 bythreads 110 as shown in FIG. 15, or may be press-fitted into the bore106 against a flange 112 formed on the tube as shown in FIG. 16.

As embodied herein, the rich air/fuel mixture is heated in the bore 106as it is drawn through this bore and the tube 108 by the sucking actionof a negative pressure working at the end of the tube when the intakevalve 24 opens. Because the short tube 108 opens near the inlet port 28,the enriched mixture, as in the other embodiments, is suppliedsubstantially only into the flow P which enters auxiliary chamber 26.Consequently, the flow P has a lowered air-to-fuel ratio, and istherefore more readily ignitable than the air/fuel mixture suppliedthrough the passage 98.

As is evident from the above, the invention, as embodied herein anddepicted in FIGS. 15 and 16, promotes atomization of the rich air/fuelmixture since it is preheated by the heat of the cylinder head, therebyensuring its ignition to a greater extent than conventionally. The shorttube 108 can be located accurately, and is less liable to be deformedunder the influence of heat and other factors. The tube 108 is alsoadvantageous in respect of servicing, inspection and maintenance becauseit may be freely fitted and detached by means of its threaded portion110, or its press-fitting.

In accordance with the invention, the short tube 108 may have its outletend flattened into an elliptical shape for directing the richer mixturemore effectively and smoothly into the inlet port 28 of the auxiliarycombustion chamber 26.

As shown in FIGS. 17 and 18, at least one side of the tube 108 may havea portion 114 flattened inwardly to form an elliptical outlet 116. Theflow of the rich air/fuel mixture along the back surface 30 of theintake valve 24 and the wall of the main combustion chamber 20 is thusdirected accurately into the inlet port 28.

Also in accordance with the invention, the short tube 108 may befabricated of a soft metal, such as copper, and the walls of the tubethinned near the outlet end of the tube for automatically adapting theoutlet tube to the recession of the outlet valve, as the valve 24 andthe valve seat 102 tend to wear in use.

The intake valve 24 normally rests on the valve seat 102, but the valveand seat sometimes wear, recessing the valve a little more deeply whenit has been used for a long time or during the running-in period. Ifthen the rich air/fuel mixture supply tube 108 is made of some materialwith high rigidity, it may impair the operation of the intake valve orprevent it from being perfectly closed. To avoid such problems, the tube108 in this invention preferably reduced in wall thickness at its outletend portion 118, and is preferably made of a relatively soft materialsuch as copper or the like. In this embodiment of the invention, thatportion 118 of the outlet end of the rich air/fuel mixture supply tube108, which contacts the intake valve 24, becomes deformed to adaptitself to the pressure thereof should the intake valve recede to agreater extent than is expected either during the initial running-inperiod or over the longer period of time the car is operated.

As is evident from the above, this embodiment maintains the seal betweenthe intake valve 24 and its valve seat 102 for a long duration byabsorbing the effect of the recession of the intake valve. In addition,this embodiment prevents the deformation of the rich air/fuel mixturesupply tube, except at the thinned edge of the tube.

In accordance with the invention, the passage through the cylinder headfor introducing the rich air/fuel mixture into the auxiliary combustionchamber may open into an annular groove formed in the wall of the leanair/fuel mixture intake and a sleeve defining a passage portion for therich mixture may be fixed in the outlet of the intake. It isadvantageous for the apparatus admitting the rich air/fuel mixture to beable to be assembled with a minimum of complexity and with a maximum offlexibility as to various types of combustion chambers and lean air/fuelintakes. It is also desirable to minimize resistance to the leanair/fuel mixture being drawn into the main combustion chamber throughthe intake valve.

As embodied herein and illustrated in FIGS. 20 and 21, the bore 106 inthe cylinder head 22, which form a passageway for the rich mixture,opens into an annular groove 120 formed in the internal wall surface ofthe lean mixture intake 98. A sleeve 122 is fitted in the intake 98 fordefining a passage 124 between an indented portion 126 formed on theperiphery of the sleeve and the wall of the intake passage 98. Thepassage portion 124 communicates with the bore 106 through the annulargroove 120. Further, end 128 of the passage 124 is positioned adjacentthe inlet port 28 in the auxiliary combustion chamber 26. Preferably,the end 128 is so disposed as to be closed by the back face 30 of theintake valve 24 when the valve is in closed position. In such case, toprevent the valve 24 from being held away from the valve seat 102 by thesleeve 122 when the valve and seat wear and the valve becomes recessed,the sleeve may be made of soft material such as thin copper metal sheet.

In this embodiment of the invention, a stream of incoming mixture(indicated by the arrow P in the drawing) is introduced into theauxiliary combustion chamber 26 through the inlet port 28 as the intakevalve 24 opens on the suction stroke. Then the residual combustion gasproduced by the preceding combustion stroke, remaining in the auxiliarycombustion chamber 26, is scavenged into the main combustion chamber 20through the outlet port 32, as indicated by the arrow Q. As the intakevalve 24 opens the end 128 of the passage portion 124 is uncovered andthe rich air/fuel mixture is drawn through the supply passage 106 andpassage 124 and becomes part of the flow P entering the auxiliarycombustion chamber 26 to ensure subsequent ignition of the mixturefollowing compression.

As embodied herein, the sleeve 122 is provided over the annular groove120 to supply the rich air/fuel mixture. Therefore, it offers muchflexibility in respect to the fitting of the sleeve and the constructionof the rich air/fuel mixture supply passage 106. Furthermore, theapparatus, according to this invention, can be fitted efficiently andapplied to various types of combustion chambers. Also, it is excellentin respect of performance and manufacture. In addition, a reduction insuction efficiency is prevented, because there is less resistance to thestream of incoming lean mixture within the intake passage 98. Further,this embodiment permits the maintaining of a tight seal between theintake valve 24 and its valve seat 102 for a long time by accommodatingthe recession of the intake valve seat by a slight deformation of thesleeve 122.

It will be apparent to those skilled in the art that variousmodifications and variations could be made in the present inventionwithout departing from the scope or spirit thereof.

What is claimed is:
 1. In an internal combustion engine having a maincombustion chamber defined by a cylinder, a cylinder head and a piston,an auxiliary combustion chamber integrally cast in the wall of thecylinder head having an unvalved inlet port and an unvalved outlet portthrough the wall of the cylinder head for communicating between theauxiliary combustion chamber and the main combustion chamber, an intakeport disposed in the cylinder head for supplying a lean air/fuel mixtureinto the main combustion chamber, an auxiliary passage disposed in theintake port for supplying a rich air/fuel mixture, an intake valveoperably disposed in the intake port for controlling the flow of theair/fuel mixtures, and an ignition spark plug provided in the auxiliarycombustion chamber, the improvement comprising:tubular insert means ofheat and corrosion-resistant material fixed in the wall of the cylinderhead within the inlet and outlet ports.
 2. The improvement of claim 1wherein said tubular inserts of heat and corrosion-resistant materialare integrally cast within said inlet and outlet ports.